Providing indirect data addressing in an input/output processing system where the indirect data address list is non-contiguous

ABSTRACT

Systems, methods and computer program products for providing indirect data addressing at an I/O subsystem of an I/O processing system. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method includes receiving a control word for an I/O operation. The control word includes an indirect data address for data associated with the I/O operation. The indirect data address includes a starting location of a list of storage addresses that collectively specify the data, the list spans two or more non-contiguous storage locations. Data is gathered responsive to the list. The gathered data is transmitted to a control unit in the I/O processing system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates generally to input/output processing, andin particular, to providing a non-contiguous indirect data addressinglist at an I/O subsystem of an I/O processing system.

2. Description of Background

Input/output (I/O) operations are used to transfer data between memoryand I/O devices of an I/O processing system. Specifically, data iswritten from memory to one or more I/O devices, and data is read fromone or more I/O devices to memory by executing I/O operations.

To facilitate processing of I/O operations, an I/O subsystem of the I/Oprocessing system is employed. The I/O subsystem is coupled to mainmemory and the I/O devices of the I/O processing system and directs theflow of information between memory and the I/O devices. One example ofan I/O subsystem is a channel subsystem. The channel subsystem useschannel paths as communications media. Each channel path includes achannel coupled to a control unit, the control unit being furthercoupled to one or more I/O devices.

The channel subsystem may employ channel command words (CCWs) totransfer data between the I/O devices and memory. A CCW specifies thecommand to be executed. For commands initiating certain I/O operations,the CCW designates the memory area associated with the operation, theaction to be taken whenever a transfer to or from the area is completed,and other options.

During I/O processing, a list of CCWs is fetched from memory by achannel. The channel parses each command from the list of CCWs andforwards a number of the commands, each command in its own entity, to acontrol unit coupled to the channel. The control unit then processes thecommands. The channel tracks the state of each command and controls whenthe next set of commands are to be sent to the control unit forprocessing. The channel ensures that each command is sent to the controlunit in its own entity. Further, the channel infers certain informationassociated with processing the response from the control unit for eachcommand.

Performing I/O processing on a per CCW basis may involve a large amountof processing overhead for the channel subsystem, as the channels parseCCWs, track state information, and react to responses from the controlunits. Therefore, it may be beneficial to shift much of the processingburden associated with interpreting and managing CCW and stateinformation from the channel subsystem to the control units. Simplifyingthe role of channels in communicating between the control units and anoperating system in the I/O processing system may increase communicationthroughput as less handshaking is performed. However, altering commandsequences, as well as roles of the channel subsystem and the controlunits, allows the amount of data that is transferred within a single I/Ooperation to more than one megabyte. This is the maximum amount of datathat can be transferred with one continuous list of transport indirectdata addresses when the system page size is 4 k bytes. Currently, anexisting Channel Command Word (CCW) cannot support a data transfer ofmore than 64 k bytes within a single I/O operation because of thelimitation of the two byte count field in the CCW. The Transport ControlWord (TCW) solved that problem by increasing the byte count to fourbytes in the TCW, but then the next limitation of one megabyte wasencountered because the transport indirect data address list (TIDAL)must be contained in one page which is 4 k bytes which only allowed 256address list entries.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention include a computer program product forproviding indirect data addressing at an input/output (I/O) subsystem ofan I/O processing system. The computer program product includes atangible storage medium readable by a processing circuit and storinginstructions for execution by the processing circuit for performing amethod. The method includes receiving a control word for an I/Ooperation. The control word includes an indirect data address for dataassociated with the I/O operation. The indirect data address includes astarting location of a list of storage addresses that collectivelyspecify the data, the list spans two or more non-contiguous storagelocations. Data is gathered responsive to the list. The gathered data istransmitted to a control unit in the I/O processing system.

Additional embodiments include an apparatus for providing indirect dataaddressing at an I/O subsystem of an I/O processing system. Theapparatus includes an I/O subsystem adapted to communicate with acontrol unit in the I/O processing system. The I/O subsystem performs amethod including receiving a control word for an I/O operation. Thecontrol word includes an indirect data address for data associated withthe I/O operation. The indirect data address includes a startinglocation of a list of storage addresses that collectively specify thedata, the list spans two or more non-contiguous storage locations. Datais gathered responsive to the list. The gathered data is transmitted tothe control unit.

Further embodiments include a method for providing indirect dataaddressing at an I/O subsystem of an I/O processing system. The methodincludes receiving a control word for an I/O operation. The control wordincludes an indirect data address for data associated with the I/Ooperation. The indirect data address includes a starting location of alist of storage addresses that collectively specify the data, the listspans two or more non-contiguous storage locations. Data is gatheredresponsive to the list. The gathered data is transmitted to a controlunit in the I/O processing system.

Still further embodiments include a computer program product forproviding indirect data addressing at an I/O subsystem of an I/Oprocessing system. The computer program product includes a tangiblestorage medium readable by a processing circuit and storing instructionsfor execution by the processing circuit for performing a method. Themethod includes receiving a control word for an I/O operation. Thecontrol word includes an indirect data address for customer data outputfrom the I/O operation. The indirect data address includes a startinglocation of a list of storage addresses that collectively specify astorage location for the customer data output, the list spans two ormore non-contiguous storage locations. Customer data output is receivedfrom a control unit in the I/O processing system in response to the I/Ooperation being executed at the control unit. The customer data outputis stored at the storage location at the I/O subsystem responsive to thelist.

Other articles of manufacture, apparatuses, and/or methods according toembodiments will be or become apparent to one with skill in the art uponreview of the following drawings and detailed description. It isintended that all such additional articles of manufacture, apparatuses,and/or methods be included within this description, be within the scopeof the present invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts one embodiment of an I/O processing system incorporatingand using one or more aspects of the present invention;

FIG. 2A depicts one example of a prior art channel command word;

FIG. 2B depicts one example of a prior art channel command word channelprogram;

FIG. 3 depicts one embodiment of a prior art link protocol used incommunicating between a channel and control unit to execute the channelcommand word channel program of FIG. 2B;

FIG. 4 depicts one embodiment of a transport control word channelprogram, in accordance with an aspect of the present invention;

FIG. 5 depicts one embodiment of a link protocol used to communicatebetween a channel and control unit to execute the transport control wordchannel program of FIG. 4, in accordance with an aspect of the presentinvention;

FIG. 6 depicts one embodiment of a prior art link protocol used tocommunicate between a channel and control unit in order to execute fourwrite commands of a channel command word channel program;

FIG. 7 depicts one embodiment of a link protocol used to communicatebetween a channel and control unit to process the four write commands ofa transport control word channel program, in accordance with an aspectof the present invention;

FIG. 8 depicts one embodiment of a control unit and a channel subsystem,in accordance with an aspect of the present invention;

FIG. 9 depicts one embodiment of a transport mode indirect data addressword (TIDAW), in accordance with an aspect of the present invention;

FIG. 10 depicts one embodiment of a process for providing non-contiguousindirect data addressing at an I/O subsystem; and

FIG. 11 depicts one embodiment of an article of manufactureincorporating one or more aspects of the present invention.

The detailed description explains the preferred embodiments of theinvention, together with advantages and features, by way of example withreference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with an aspect of the present invention, input/output(I/O) processing is facilitated. I/O processing is facilitated, in oneexample, by reducing communications between components of an I/Oprocessing system used to perform the I/O processing. For instance, thenumber of exchanges and sequences between an I/O communications adapter,such as a channel, and a control unit is reduced. This is accomplishedby sending a plurality of commands from the I/O communications adapterto the control unit as a single entity for execution by the controlunit, and by the control unit sending the data resulting from thecommands, if any, as a single entity.

The plurality of commands are included in a block, referred to herein asa transport command control block (TCCB), an address of which isspecified in a transport control word (TCW). The TCW is sent from anoperating system (OS) or other application to the I/O communicationsadapter, which in turn forwards the TCCB in a command message to thecontrol unit for processing. The control unit processes each of thecommands absent a tracking of status relative to those individualcommands by the I/O communications adapter. The plurality of commands isalso referred to as a channel program, which is parsed and executed onthe control unit rather than the I/O communications adapter.

In an exemplary embodiment, the TCW for an I/O operation includespointers indicating the location of the control data (e.g., the TCCB)and the customer data associated with the I/O operation. In an exemplaryembodiment, the pointers refer to an indirect data address, referred toherein as a transport mode indirect data address list (TIDAL). The TIDALincludes a list of addresses where the data is located; these addressesare referred to herein as transport mode indirect data address words(TIDAWs). In the current system design with 4K pages the TIDAL cannot belarger than four kilobytes (4K), thus limiting the number of continuousTIDAWs that may be included in a single TIDAL to 256 (each TIDAL is 16bytes). This limits the total amount of data that can be transferred byone I/O operation to one megabyte assuming 4K pages, each TIDAL is 16bytes and the TIDAL has to be contained in one 4K page. In an exemplaryembodiment of the present invention, this limitation is removed byallowing a TIDAW address to indicate the starting location of the nextTIDAWs at another storage location which may be in a different page. Aflag in the TIDAW is utilized to indicate whether the address of theTIDAW includes a data address or an address of the continuation of theTIDAW list. In this manner, TIDAWs making up a single TIDAL can belocated in non-contiguous storage locations and thus, more than 256TIDAWs can be included in a single TIDAL list. This allows more data tobe transferred within a single I/O operation. For example, in anexemplary embodiment, where the count field in the TCW is four bytes,about four gigabytes (four gigabytes minus one byte) may be transferredwithin a single I/O operation.

One example of an I/O processing system incorporating and using one ormore aspects of the present invention is described with reference toFIG. 1. I/O processing system 100 includes a host system 101, whichfurther includes for instance, a main memory 102, one or more centralprocessing units (CPUs) 104, a storage control element 106, and achannel subsystem 108. The host system 101 may be a large scalecomputing system, such as a mainframe or server. The I/O processingsystem 100 also includes one or more control units 110 and one or moreI/O devices 112, each of which is described below.

Main memory 102 stores data and programs, which can be input from I/Odevices 112. For example, the main memory 102 may include one or moreoperating systems (OSs) 103 that are executed by one or more of the CPUs104. For example, one CPU 104 can execute a Linux® operating system 103and a z/OS® operating system 103 as different virtual machine instances.The main memory 102 is directly addressable and provides for high-speedprocessing of data by the CPUs 104 and the channel subsystem 108.

CPU 104 is the controlling center of the I/O processing system 100. Itcontains sequencing and processing facilities for instruction execution,interruption action, timing functions, initial program loading, andother machine-related functions. CPU 104 is coupled to the storagecontrol element 106 via a connection 114, such as a bidirectional orunidirectional bus.

Storage control element 106 is coupled to the main memory 102 via aconnection 116, such as a bus; to CPUs 104 via connection 114; and tochannel subsystem 108 via a connection 118. Storage control element 106controls, for example, queuing and execution of requests made by CPU 104and channel subsystem 108.

In an exemplary embodiment, channel subsystem 108 provides acommunication interface between host system 101 and control units 110.Channel subsystem 108 is coupled to storage control element 106, asdescribed above, and to each of the control units 110 via a connection120, such as a serial link. Connection 120 may be implemented as anoptical link, employing single-mode or multi-mode waveguides in a FibreChannel fabric. Channel subsystem 108 directs the flow of informationbetween I/O devices 112 and main memory 102. It relieves the CPUs 104 ofthe task of communicating directly with the I/O devices 112 and permitsdata processing to proceed concurrently with I/O processing. The channelsubsystem 108 uses one or more channel paths 122 as the communicationlinks in managing the flow of information to or from I/O devices 112. Asa part of the I/O processing, channel subsystem 108 also performs thepath-management functions of testing for channel path availability,selecting an available channel path 122 and initiating execution of theoperation with the I/O devices 112.

Each channel path 122 includes a channel 124 (channels 124 are locatedwithin the channel subsystem 108, in one example, as shown in FIG. 1),one or more control units 110 and one or more connections 120. Inanother example, it is also possible to have one or more dynamicswitches (not depicted) as part of the channel path 122. A dynamicswitch is coupled to a channel 124 and a control unit 110 and providesthe capability of physically interconnecting any two links that areattached to the switch. In another example, it is also possible to havemultiple systems, and therefore multiple channel subsystems (notdepicted) attached to control unit 110.

Also located within channel subsystem 108 are subchannels (not shown).One subchannel is provided for and dedicated to each I/O device 112accessible to a program through the channel subsystem 108. A subchannel(e.g., a data structure, such as a table) provides the logicalappearance of a device to the program. Each subchannel providesinformation concerning the associated I/O device 112 and its attachmentto channel subsystem 108. The subchannel also provides informationconcerning I/O operations and other functions involving the associatedI/O device 112. The subchannel is the means by which channel subsystem108 provides information about associated I/O devices 112 to CPUs 104,which obtain this information by executing I/O instructions.

Channel subsystem 108 is coupled to one or more control units 110. Eachcontrol unit 110 provides logic to operate and control one or more I/Odevices 112 and adapts, through the use of common facilities, thecharacteristics of each I/O device 112 to the link interface provided bythe channel 124. The common facilities provide for the execution of I/Ooperations, indications concerning the status of the I/O device 112 andcontrol unit 110, control of the timing of data transfers over thechannel path 122 and certain levels of I/O device 112 control.

Each control unit 110 is attached via a connection 126 (e.g., a bus) toone or more I/O devices 112. I/O devices 112 receive information orstore information in main memory 102 and/or other memory. Examples ofI/O devices 112 include card readers and punches, magnetic tape units,direct access storage devices, displays, keyboards, printers, pointingdevices, teleprocessing devices, communication controllers and sensorbased equipment, to name a few.

One or more of the above components of the I/O processing system 100 arefurther described in “IBM® z/Architecture Principles of Operation,”Publication No. SA22-7832-05, 6th Edition, April 2007; U.S. Pat. No.5,461,721 entitled “System For Transferring Data Between I/O Devices AndMain Or Expanded Storage Under Dynamic Control Of Independent IndirectAddress Words (IDAWS),” Cormier et al., issued Oct. 24, 1995; and U.S.Pat. No. 5,526,484 entitled “Method And System For Pipelining TheProcessing Of Channel Command Words,” Casper et al., issued Jun. 11,1996, each of which is hereby incorporated herein by reference in itsentirety. IBM is a registered trademark of International BusinessMachines Corporation, Armonk, N.Y., USA. Other names used herein may beregistered trademarks, trademarks or product names of InternationalBusiness Machines Corporation or other companies.

In one embodiment, to transfer data between I/O devices 112 and memory102, channel command words (CCWs) are used. A CCW specifies the commandto be executed, and includes other fields to control processing. Oneexample of a CCW is described with reference to FIG. 2A. A CCW 200includes, for instance, a command code 202 specifying the command to beexecuted (e.g., read, read backward, control, sense and write); aplurality of flags 204 used to control the I/O operation; for commandsthat specify the transfer of data, a count field 206 that specifies thenumber of bytes in the storage area designated by the CCW to betransferred; and a data address 208 that points to a location in mainmemory that includes data, when direct addressing is employed, or to alist (e.g., contiguous list) of modified indirect data address words(MIDAWs) to be processed, when modified indirect data addressing isemployed. Modified indirect addressing is further described in U.S.application Ser. No. 11/464,613, entitled “Flexibly Controlling TheTransfer Of Data Between Input/Output Devices And Memory,” Brice et al.,filed Aug. 15, 2006, which is hereby incorporated herein by reference inits entirety.

One or more CCWs arranged for sequential execution form a channelprogram, also referred to herein as a CCW channel program. The CCWchannel program is set up by, for instance, an operating system, orother software. The software sets up the CCWs and obtains the addressesof memory assigned to the channel program. An example of a CCW channelprogram is described with reference to FIG. 2B. A CCW channel program210 includes, for instance, a define extent CCW 212 that has a pointer214 to a location in memory of define extent data 216 to be used withthe define extent command. In this example, a transfer in channel (TIC)218 follows the define extent command that refers the channel program toanother area in memory (e.g., an application area) that includes one ormore other CCWs, such as a locate record 217 that has a pointer 219 tolocate record data 220, and one or more write CCWs 221. Each write CCW220 has a pointer 222 to a data area 224. The data area includes anaddress to directly access the data or a list of data address words(e.g., MIDAWs or IDAWs) to indirectly access the data. Further, CCWchannel program 210 includes a predetermined area in the channelsubsystem defined by the device address called the subchannel for status226 resulting from execution of the CCW channel program.

The processing of a CCW channel program is described with reference toFIG. 3, as well as with reference to FIG. 2B. In particular, FIG. 3shows an example of the various exchanges and sequences that occurbetween a channel and a control unit when a CCW channel program isexecuting. The link protocol used for the communications is FICON (FibreConnectivity), in this example. Information regarding FICON is describedin “Fibre Channel Single Byte Command Code Sets-3 Mapping Protocol(FC-SB-3), T11/Project 1357-D/Rev. 1.6, INCITS (March 2003), which ishereby incorporated herein by reference in its entirety.

Referring to FIG. 3, a channel 300 opens an exchange with a control unit302 and sends a define extent command and data associated therewith 304to control unit 302. The command is fetched from define extent CCW 212(FIG. 2B) and the data is obtained from define extent data area 216. Thechannel 300 uses TIC 218 to locate the locate record CCW and the writeCCW. It fetches the locate record command and data 306 (FIG. 3) from thelocate record CCW 217 (FIG. 2B) and locate record data 220. The writecommand and data 308 (FIG. 3) is fetched from write CCW 221 and dataarea 224 (FIG. 2B). Each is sent to the control unit 302.

The control unit 302 opens an exchange 310 with the channel 300, inresponse to the open exchange of the channel 300. This can occur beforeor after locate command and data 306 and/or write command and data 308.Along with the open exchange, a response (CMR) is forwarded to thechannel 300. The CMR provides an indication to the channel 300 that thecontrol unit 302 is active and operating.

The control unit 302 provides the status to the channel 300 and closesthe exchange 312. In response thereto, the channel 300 stores the data,examines the status and closes the exchange 314, which indicates to thecontrol unit 302 that the status has been received.

The processing of the above CCW channel program to write 4 k of datarequires two exchanges to be opened and closed and six sequences. Thetotal number of exchanges and sequences between the channel and controlunit is reduced through collapsing multiple commands of the channelprogram into a TCCB. The channel, e.g., channel 124 of FIG. 1, uses aTCW to identify the location of the TCCB, as well as locations foraccessing and storing status and data associated with executing thechannel program. The TCW is interpreted by the channel and is not sentor seen by the control unit.

One example of a channel program to write 4 k of data, as in FIG. 2B,but includes a TCCB, instead of separate individual CCWs, is describedwith reference to FIG. 4. As shown, a channel program 400, referred toherein as a TCW channel program, includes a TCW 402 specifying alocation in memory of a TCCB 404, as well as a location in memory of adata area 406 or a TIDAL 410 (i.e., a list of transport mode indirectdata address words (TIDAWs), similar to MIDAWs) that points to data area406, and a status area 408. TIDAW zero 412, TIDAW one 414 and TIDAW two416 (collectively TIDAWs 412-416) can reference different locations inthe data area 406 for acquiring or storing data. The TIDAWs 412-416 canreference non-contiguous blocks of data or contiguous blocks of data.The TIDAWs 412-416 in TIDAL 410 may be located sequentially in memory orlocated non-contiguously relative to each other. While only three TIDAWs412-416 are depicted in TIDAL 410, it will be understood that any numberof TIDAWs can be included in the TIDAL 410.

The processing of a TCW channel program is described with reference toFIG. 5. The link protocol used for these communications is, forinstance, Fibre Channel Protocol (FCP). In particular, three phases ofthe FCP link protocol are used, allowing host bus adapters to be usedthat support FCP to perform data transfers controlled by CCWs. FCP andits phases are described further in “Information Technology—FibreChannel Protocol for SCSI, Third Version (FCP-3),” T10 Project 1560-D,Revision 4, Sep. 13, 2005, which is hereby incorporated herein byreference in its entirety.

Referring to FIG. 5, a channel 500 opens an exchange with a control unit502 and sends TCCB 504 to the control unit 502. In one example, the TCCB504 and sequence initiative are transferred to the control unit 502 in aFCP command, referred to as FCP_CMND information unit (IU) or atransport command IU. The control unit 502 transmits a transfer ready(XFER_RDY) IU 510 to the channel 500 when it is ready to receive datafor the write commands received in the TCCB 504. In response toreceiving the XFER_RDY IU 510, the channel 500 transfers the data 506 tothe control unit 502, via, for instance, a FCP_Data IU. The control unit502 executes the multiple commands of the TCCB 504 (e.g., define extentcommand, locate record command, write command as device control words(DCWs)) and writes the data 506 received from the channel 500. It alsoprovides status and closes the exchange 508. As one example, finalstatus is sent in a FCP status frame that has a bit active in, forinstance, byte 10 or 11 of the payload of a FCP_RSP IU, also referred toas a transport response IU. The FCP_RSP IU payload may be used totransport FICON ending status along with additional status information.

The embodiment of the link protocol depicted in FIG. 5 is utilized whenXFER_RDY is enabled. In the embodiment depicted in FIG. 5, the channel500 cannot send the data 506 to the control unit 502 until it isrequested by the control unit 502 via the XFER_RDY IU 510. In analternate exemplary embodiment, XFER_RDY is disabled and the controlunit does not transmit a XFER_RDY IU 510 to the channel 500. Thus, thechannel 500 does not have to wait for the control unit 502 to requestthe data 506 before sending the data 506. This alternate embodiment,where XFER_RDY is disabled may be utilized when the channel 500 and thecontrol unit 502 are located geographically far apart from each other(e.g., greater than twenty kilometers, greater than fifty kilometers) toimprove performance. Unless otherwise specified, the discussion hereinassumes that XFER_RDY is enabled.

In a further example, to write 4K of customer data, the channel 500 usesthe FCP link protocol phases, as follows:

1. Transfer a TCCB in the FCP_CMND IU and sequence initiative to thecontrol unit 502.

2. Wait for a XFER_RDY IU indicating that the control unit is ready toreceive the data.

3. Transfer the IU of data, and sequence initiative to the control unit502.

4. Final status is sent in a FCP status frame that has a bit active in,for instance, byte 10 or 11 of the FCP_RSP IU Payload. The FCP_RSP_INFOfield or sense field is used to transport FICON ending status along withadditional status information.

By executing the TCW channel program of FIG. 4, there is only oneexchange opened and closed (see also FIG. 5), instead of two exchangesfor the CCW channel program of FIG. 2B (see also FIG. 3). Further, forthe TCW channel program, there are four communication sequences (seeFIGS. 4-5), as compared to six sequences for the CCW channel program(see FIGS. 2B-3).

The number of exchanges and sequences remain the same for a TCW channelprogram, even if additional commands are added to the program. Compare,for example, the communications of the CCW channel program of FIG. 6with the communications of the TCW channel program of FIG. 7. In the CCWchannel program of FIG. 6, each of the commands (e.g., define extentcommand and data 600, locate record command and data 601, write commandand data 602, write command and data 604, locate record command and data606, write command and data 608, and write command and data 620) aresent in separate sequences from channel 610 to control unit 612. ThisCCW channel program requires two exchanges to be opened and closed(e.g., open exchanges 622, 624 and close exchanges 626, 628), and tencommunications sequences. This is compared to the four sequences and oneexchange for the TCW channel program of FIG. 7, which accomplishes thesame task as the CCW channel program of FIG. 6.

As depicted in FIG. 7, a channel 700 opens an exchange with a controlunit 702 and sends a TCCB 704 to the control unit 702. The TCCB 704includes the define extent command, the two locate record commands, andthe four write commands in DCWs, as described above. Similar to theexample depicted in FIG. 5, the control unit 702 may use an XFER_RDY IU710 to notify the channel 700 that it is ready receive data, providedthat XFER_RDY support is not disabled. The channel 700 transmits 16 k ofdata 706 to the control unit 702 in a single sequence upon receipt ofthe XFER_RDY IU 710. The channel 700 inserts a CRC every 4K of the 16 kof data 706 in the sequence. The insertion of a CRC every 4K allows thecontrol unit 702 to verify the 16K of data incrementally, rather thanbuffer the entire 16K for verification before completing the writecommands in the TCCB 704. Additionally, the control unit 702 providesstatus to the channel 700 and closes the exchange 708. Thus, the TCWchannel program of FIG. 7 requires much less communications to transferthe same amount of data as the CCW channel program of FIG. 6, whilesupporting incremental data verification via multiple CRC insertion inthe output data stream from the channel 700.

Turning now to FIG. 8, one embodiment of channel 124 in the channelsubsystem 108 and the control unit 110 of FIG. 1 that support TCWchannel program execution are depicted in greater detail. The controlunit 110 includes CU control logic 802 to parse and process messagescontaining a TCCB, such as the TCCB 704 of FIG. 7, as well as datareceived from the channel 124 via the connection 120. The CU controllogic 802 can extract DCWs and control data from the TCCB received atthe control unit 110 to control a device, for instance, I/O device 112via connection 126. The CU control logic 802 sends device commands anddata to the I/O device 112, and receives status information and otherfeedback from the I/O device 112. When the CU control logic 802 receivesdata, such as the first checking block boundary of the 16K bytes of data706 of FIG. 7, the CU control logic 802 writes this data received intodata buffer 804 for temporary storage, until the CRC is received for thechecking block boundary is checked, then that data may be sent to theI/O device 112. This continues for each checking block boundary untilthe I/O operation is completed.

The control unit 110 may further include other queue or memory elements(not depicted) for storing additional message or status informationassociated with communications between the channel 124 and the I/Odevice 112.

The channel 124 in the channel subsystem 108 includes elements tosupport communication with the control unit 110. For example, thechannel 124 may include CHN control logic 806 that interfaces with thegather data logic 812. The gather data logic 812 is described hereinbelow in reference to FIG. 10. In an exemplary embodiment, the CHNcontrol logic 806 controls communication between the channel subsystem108 and the control unit 110. The CHN control logic 806 may directlyinterface to the CU control logic 802 via the connection 120 to sendcommands and receive responses, such as transport commands and responseIUs. Alternatively, messaging interfaces and/or additional buffers (notdepicted) can be placed between the CHN control logic 806 and the CUcontrol logic 802. The CHN subsystem registers 814 can include fixedvalues that provide configuration and status information, as well asdynamic status information, updated as commands are transported andresponses are received. The CHN subsystem registers 814 may be dedicatedhardware registers and/or virtual registers established using memorymapping.

In one embodiment, the CHN subsystem registers 814 include the TIDAL 410and TIDAWs 412-416 of FIG. 4 as memory mapped registers.

One example of a TIDAW 900 is depicted in FIG. 9. The TIDAW 900 providesindirect addressing to data used in a TCW channel program, such as theTIDAWs 412-416 of FIG. 4. The TIDAW 900 includes flags 902, a count 904,and an address 906. Each field (i.e., flags 902, count 904, and address906) in the TIDAW format 900 is assigned to a particular byte address tosupport parsing of the fields. Although one arrangement of fields withinthe TIDAW 900 is depicted in FIG. 9, it will be understood that theorder of fields can be rearranged to alternate orderings.

In an exemplary embodiment, the flags 902 include a last TIDAW flag anda transport-transfer in channel (T-TIC) flag, in addition to otherflags. The last TIDAW flag indicates that the associated TIDAW is thelast TIDAW in a TIDAL, consistent with the definition for a MIDAW. Whencount 904 goes to zero with the last TIDAW flag set, the data transferfor the associated I/O operation is complete. The T-TIC flag indicateswhether the contents of the address 906 include data or the address ofthe next TIDAW in the TIDAL. In an exemplary embodiment, when the T-TICflag is set, then the address 906 in the TIDAW is the address of thenext TIDAW in the TIDAL. In the manner, the address 906 may be utilizedto access a TIDAW at a non-contiguous storage location from the currentTIDAW. Thus, the TIDAW list can contain more than 256 entries, therebyexceeding the maximum number of allowable indirect data address words incurrent implementations. In an exemplary embodiment, when the T-TIC flagis set the address 906 must have the four low order bits set to zerobecause the 16 byte TIDAW must be on a 16 byte address boundary. Whenthe T-TIC flag is not set, then the address 906 in the TIDAW is theaddress of a portion of the data that makes up the data being gatheredfor the I/O operation. The size of the data is indicated in the countfield 904. If the last TIDAW flag and the T-TIC flag are not set, thenthe next TIDAW is located in the next storage location (e.g., it iscontiguous to the current TIDAW).

Turning now to FIG. 10, a process 1000 for gathering data for an I/Ooperation will now be described in accordance with exemplaryembodiments, and in reference to the I/O processing system 100 ofFIG. 1. At block 1002, the channel subsystem 108 receives a control wordfor an I/O operation (e.g., a TCW). The control word includes anindirect data address that points to the starting address of a list ofstorage addresses (e.g., a TIDAL having multiple TIDAWs) that make upthe data utilized by the by the I/O operation. In exemplary embodiments,the data is customer data (e.g., data input or output from the I/Ooperation). In alternate exemplary embodiments, the data is control data(e.g., a TCCB). In an exemplary embodiment, the list of storageaddresses spans two or more non-contiguous storage locations.

At block 1004, the data is gathered by instructions located at thechannel subsystem 108. The gathering is based on the contents of thelist. In an exemplary embodiment, each entry in the list (e.g., eachTIDAW) includes both a storage address and a T-TIC flag to indicatewhether the storage address is the location of a portion of the data, orwhether the storage address points to the location of another portion ofthe list containing more storage addresses. In this manner, a singleTIDAL can be contained in multiple pages removing any restraints on thelength of the TIDAL. When the T-TIC flag indicates that the storageaddress is the location of a portion of the data (e.g., the T-TIC flagis not set), then the data at the storage location is accessed and addedto the data. This adding of new data can be performed in any mannerknown in the art, such as merging with data already gathered, appendingto data already gathered, etc.

When the T-TIC flag indicates that the current storage address is thelocation of another portion of the list, then processing continues byaccessing a new TIDAW located at the specified storage location. Data atthe storage location specified in the new TIDAW is accessed and added tothe data. In an exemplary embodiment, the TIDAW includes a count 904 tospecify how much data to read (or write) from each storage address. Whena TIDAW with the last TIDAW flag is set the gathering is completed.Otherwise, the next TIDAW is accessed and the data gathering continues.

At block 1006, the data is transmitted to a control unit 110 by thechannel subsystem 108.

Technical effects of exemplary embodiments include providingnon-contiguous indirect data addressing at a I/O subsystem. By allowingmultiple 4 k byte pages to contain the list of storage addresses (TIDAL)allows the number of TIDAWs to be unlimited, therefore more data can beassociated with a single I/O operation. Large transfers of data canreduce communication overhead by avoiding additional handshaking andother delays associated with multiple smaller messages.

The following examples depict manners in which exemplary embodiments maybe utilized to perform more than moving large blocks of data.

Exemplary embodiments may be utilized to aid in the prefixing of achannel program by an operating system. For example, when a channelprogram is passed to an operating system, the operating system maymodify the channel program to add, replace, or modify command CCWs orDCWs. In an exemplary embodiment, this implies that a TCCB TIDAL will becreated where the first TIDAW points to an area of storage containingthe first part of the modified TCCB. The second TIDAW points to theremainder of the unmodified TCCB.

Exemplary embodiments may also be used to aid in the prefixing ofchannel programs by a hypervisor. If the hypervisor needs to modify thechannel program, it would need to create a TIDAL with one more entrythan the one passed by the guest. If the TIDAL passed by the guest isalready the maximum size (256 TIDAWs), then the hypervisor can make itsown modifications by creating a TCCB TIDAL that has two TIDAWs, one ofwhich is the T-TICs to the first TIDAW of the TIDAL passed by the guest.

TIDAL T-TICs can also ease storage requirements for operating systems.If the channel program containing a TCCB TIDAL needs to be modified, ittakes less storage to create a TIDAW and T-TIC than to allocated storagefor the caller's TCCB TIDAL plus one more TIDAW.

As described above, embodiments can be embodied in the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. In exemplary embodiments, the invention is embodied incomputer program code executed by one or more network elements.Embodiments include a computer program product 1100 as depicted in FIG.11 on a computer usable medium 1102 with computer program code logic1104 containing instructions embodied in tangible media as an article ofmanufacture. Exemplary articles of manufacture for computer usablemedium 1102 may include floppy diskettes, CD-ROMs, hard drives,universal serial bus (USB) flash drives, or any other computer-readablestorage medium, wherein, when the computer program code logic 1104 isloaded into and executed by a computer, the computer becomes anapparatus for practicing the invention. Embodiments include computerprogram code logic 1104, for example, whether stored in a storagemedium, loaded into and/or executed by a computer, or transmitted oversome transmission medium, such as over electrical wiring or cabling,through fiber optics, or via electromagnetic radiation, wherein, whenthe computer program code logic 1104 is loaded into and executed by acomputer, the computer becomes an apparatus for practicing theinvention. When implemented on a general-purpose microprocessor, thecomputer program code logic 1104 segments configure the microprocessorto create specific logic circuits.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims. Moreover, the use of the terms first, second, etc. do not denoteany order or importance, but rather the terms first, second, etc. areused to distinguish one element from another. Furthermore, the use ofthe terms a, an, etc. do not denote a limitation of quantity, but ratherdenote the presence of at least one of the referenced item.

1. A computer program product for providing indirect data addressing atan input/output (I/O) subsystem of an I/O processing system, thecomputer program product comprising: a tangible storage medium readableby a processing circuit and storing instructions for execution by theprocessing circuit for performing a method comprising: receiving acontrol word for an I/O operation, the control word including anindirect data address for data associated with the I/O operation, theindirect data address including a starting location of a list of storageaddresses that collectively specify the data, wherein two successivelist entries are located contiguously when a first of said twosuccessive entries comprises a not-set first flag and are locatednon-contiguously when the first of said two successive entries comprisesa set first flag; gathering the data, wherein gathering comprisesaccessing entries of the list until a last entry is accessed, whereinaccessing includes 1) and 2): 1) responsive to an entry of the listcomprising, the not-set first flag and a corresponding first storageaddress, gathering data from a corresponding storage location; and 2)responsive to an entry of the list comprising, the set first flag and acorresponding second storage address, obtaining a next entry of the listfrom a second storage location; and transmitting the gathered data to acontrol unit in the I/O processing system.
 2. The computer programproduct of claim 1 wherein the list of storage addresses includestransport mode indirect data address words (TIDAWs), the first storageaddress refers to a portion of the data and the second storage addressrefers to the second storage location where additional storage addressesin the list are located.
 3. The computer program product of claim 1wherein for each storage address on the list, the gathering includes:responsive to an entry of the list comprising the not-set first flag,adding contents from the first storage address to the data; responsiveto an entry of the list comprising the set first flag, accessing thesecond storage address and a second flag located at the second storageaddress, and adding contents from the second storage address to the datain response to the second flag being a not-set second flag.
 4. Thecomputer program product of claim 1 wherein the list further includes acount field associated with each storage address in the list, the countfield indicating a number of bytes to read from the storage address andthe gathering is responsive to the count fields and to the storageaddresses.
 5. The computer program product of claim 1 wherein thecontrol word is a transport control word (TCW) configured to specify alocation in memory of a transport command control block (TCCB), the TCCBconfigured to hold a plurality of commands for performing an I/Ooperation, and the list of storage addresses is a transport indirectdata address list (TIDAL).
 6. The computer program product of claim 1wherein the I/O subsystem is a channel subsystem.
 7. The computerprogram product of claim 1 wherein the control word includes a flag toindicate that it includes an indirect data address.
 8. The computerprogram product of claim 1 wherein the method further comprises,responsive to an entry of the list comprising a set last entry flag,determining that the entry is a last entry to be accessed.
 9. Thecomputer program product of claim 1 wherein the data includes at leastone of control data and customer data.
 10. An apparatus for providingindirect data addressing at an I/O subsystem of an I/O processingsystem, the apparatus comprising: an I/O subsystem adapted tocommunication with a control unit in the I/O processing system, the I/Osubsystem configured to perform a method comprising: receiving a controlword for an I/O operation, the control word including an indirect dataaddress for data associated with the I/O operation, the indirect dataaddress including a starting location of a list of storage addressesthat collectively specify the data, wherein two successive list entriesare located contiguously when a first of said two successive entriescomprises a not-set first flag and are located non-contiguously when thefirst of said two successive entries comprises a set first flag;gathering the data, wherein gathering comprises accessing entries of thelist until a last entry is accessed, wherein accessing includes 1) and2): 1) responsive to an entry of the list comprising, the not-set firstflag and a corresponding first storage address, gathering data from acorresponding storage location; and 2) responsive to an entry of thelist comprising, the set first flag and a corresponding second storageaddress, obtaining a next entry of the list from a second storagelocation; and transmitting the gathered data to the control unit. 11.The apparatus of claim 10 wherein the list of storage addresses includestransport mode indirect data address words (TIDAWs), the first storageaddress refers to a portion of the data and the second storage addressrefers to the second storage location where additional storage addressesin the list are located.
 12. The apparatus of claim 10 wherein for eachstorage address on the list, the gathering includes: responsive to anentry of the list comprising the not-set first flag, adding contentsfrom the first storage address to the data; responsive to an entry ofthe list comprising the set first flag, accessing the second storageaddress and a second flag located at the second storage address, andadding contents from the second storage address to the data in responseto the second flag being a not-set second flag.
 13. The apparatus ofclaim 10 wherein the list further includes a count field associated witheach storage address in the list, the count field indicating a number ofbytes to read from the storage address and the gathering is responsiveto the count fields and to the storage addresses.
 14. The apparatus ofclaim 10 wherein the data includes one or both of control data andcustomer data.
 15. The apparatus of claim 10 wherein the I/O subsystemis a channel subsystem that is included in a host system, and an I/Ocommunications adapter in the channel subsystem is adapted tocommunicate with the control unit via a fibre channel network using aFICON protocol.
 16. A method for providing indirect data addressing atan I/O subsystem of an I/O processing system, the method comprising:receiving a control word for an I/O operation at the I/O subsystem, thecontrol word including an indirect data address for data associated withthe I/O operation, the indirect data address including a startinglocation of a list of storage addresses that collectively specify thedata, wherein two successive list entries are located contiguously whena first of said two successive entries comprises a not-set first flagand are located non-contiguously when the first of said two successiveentries comprises a set first flag; gathering the data, whereingathering comprises accessing entries of the list until a last entry isaccessed, wherein accessing includes 1) and 2): 1) responsive to anentry of the list comprising, the not-set first flag and a correspondingfirst storage address, gathering data from a corresponding storagelocation; and 2) responsive to an entry of the list comprising, the setfirst flag and a corresponding second storage address, obtaining a nextentry of the list from a second storage location; transmitting thegathered data to a control unit in the I/O processing system.
 17. Themethod of claim 16 wherein the list of storage addresses includestransport mode indirect data address words (TIDAWs), the first storageaddress refers to a portion of the data and the second storage addressrefers to the storage location where additional storage addresses in thelist are located.
 18. The method of claim 16 wherein for each storageaddress on the list, the gathering includes: responsive to an entry ofthe list comprising the not-set first flag, adding contents from thefirst storage address to the data; responsive to an entry of the listcomprising the set first flag, accessing the second storage address anda second flag located at the second storage address, and adding contentsfrom the second storage address to the data in response to the secondflag being a not-set second flag.
 19. The method of claim 16 wherein thelist further includes a count field associated with each storage addressin the list, the count field indicating a number of bytes to read fromthe storage address and the gathering is responsive to the count fieldsand to the storage addresses.
 20. The method of claim 16 furthercomprising, responsive to an entry of the list comprising a set lastentry flag, determining that the entry is a last entry to be accessed.21. The method of claim 16 wherein the data includes at least one ofcontrol data and customer data.
 22. A computer program product forproviding indirect data addressing at an I/O subsystem of an I/Oprocessing system, the computer program product comprising: a tangiblestorage medium readable by a processing circuit and storing instructionsfor execution by the processing circuit for performing a methodcomprising: receiving a control word for an I/O operation, the controlword including an indirect data address for customer data output fromthe I/O operation, the indirect data address including a startinglocation of a list of storage addresses in the form of transport modeindirect data address words (TIDAWs) that collectively specify a storagelocation for the customer data output, wherein two successive TIDAWs arelocated contiguously when a first of said two successive entriescomprises a not-set first flag and are located non-contiguouslycontiguously when the first of said two successive entries comprises aset first flag; receiving the customer data output from a control unitin the I/O processing system in response to the I/O operation beingexecuted at the control unit; and storing the customer data output atthe storage location at the I/O subsystem responsive to the list,wherein the storage location includes at least one of: 1) responsive toan entry of the list comprising, the not-set first flag and acorresponding first storage address, a first storage locationcorresponding to the corresponding first storage address; and 2)responsive to an entry of the list comprising, the set first flag and acorresponding second storage address, a second storage locationspecified by a next entry of the list obtainable from a storage locationcorresponding to the corresponding second storage address.
 23. A methodfor providing indirect data addressing at an I/O subsystem of an I/Oprocessing system, the method comprising: receiving a control word foran I/O operation, the control word including an indirect data addressfor customer data output from the I/O operation, the indirect dataaddress including a starting location of a list of storage addresses inthe form of transport mode indirect data address words (TIDAWs) thatcollectively specify a storage location for the customer data output,wherein two successive TIDAWs are located contiguously when a first ofsaid two successive entries comprises a not-set first flag and arelocated non-contiguously when the first of said two successive entriescomprises a set first flag; receiving the customer data output from acontrol unit in the I/O processing system in response to the I/Ooperation being executed at the control unit; and storing the customerdata output at the storage location at the I/O subsystem responsive tothe list, wherein the storage location includes at least one of: 1)responsive to an entry of the list comprising, the not-set first flagand a corresponding first storage address, a first storage locationcorresponding to the corresponding first storage address; and 2)responsive to an entry of the list comprising, the set first flag and acorresponding second storage address, a second storage locationspecified by a next entry of the list obtainable from a storage locationcorresponding to the corresponding second storage address.
 24. Anapparatus for providing indirect data addressing at an I/O subsystem ofan I/O processing system, the apparatus comprising: an I/O subsystemadapted to communication with a control unit in the I/O processingsystem, the I/O subsystem configured to perform a method comprising:receiving a control word for an I/O operation, the control wordincluding an indirect data address for customer data output from the I/Ooperation, the indirect data address including a starting location of alist of storage addresses in the form of transport mode indirect dataaddress words (TIDAWs) that collectively specify a storage location forthe customer data output, wherein two successive TIDAWs are locatedcontiguously when a first of said two successive entries comprises anot-set first flag and are located non-contiguously when the first ofsaid two successive entries comprises a set first flag; receiving thecustomer data output from a control unit in the I/O processing system inresponse to the I/O operation being executed at the control unit; andstoring the customer data output at the storage location at the I/Osubsystem responsive to the list, wherein the storage location includesat least one of: 1) responsive to an entry of the list comprising, thenot-set first flag and a corresponding first storage address, a firststorage location corresponding to the corresponding first storageaddress; and 2) responsive to an entry of the list comprising, the setfirst flag and a corresponding second storage address, a second storagelocation specified by a next entry of the list obtainable from a storagelocation corresponding to the corresponding second storage address.